Generally, an integrated circuit (IC) refers to a set of electronic devices, e.g., transistors formed on a small chip of semiconductor material, typically, silicon. Typically, an interconnect structure incorporated into the IC includes one or more levels of metal lines to connect the electronic devices of the IC to one another and to external connections. An interlayer dielectric is placed between the metal levels of the IC for insulation. Generally, the efficiency of the interconnect structure depends on the resistance of each metal line and the coupling capacitance generated between the metal lines. Typically, to reduce the resistance and increase the IC performance, copper interconnect structures are used.
As the size of the IC decreases, the spacing between the metal lines decreases. This leads to increase in the coupling capacitance between the metal lines. Increase in the coupling capacitance between the metal lines has a negative impact on signal transmission along metal lines. Furthermore, increase in the coupling capacitance increases energy consumption of the integrated circuit.
One conventional technique to reduce the capacitive coupling between adjacent metal lines involves replacing a high k dielectric material that separates the metal lines with a low k dielectric material. Another conventional technique to reduce the capacitive coupling involves forming an air gap between adjacent metal lines.
Conventional techniques cannot typically prevent the unlanded via from punching through the air gap that causes shorts. Typically in the conventional techniques, a hard mask is deposited that blocks the air gap etch in the underlying interconnect layer above which the next interconnect layer via lands.
As the backend interconnect pitch becomes smaller, the regions that need to be masked to prevent etching of the air gap become closer. Generally, the conventional techniques that involve masking off vias locally do not scale with pitch. Typically, the mask layer patterning requires multiple lithography passes and complicated Optical proximity correction OPC) that significantly increases manufacturing cost and reduces yield.